I just accepted an offer at one school (yay!), but already had airfare booked for another interview next week. I don't want to waste their time (or mine) by going to this other interview, and I know they would save money on the hotel/incidental purchases by me not coming out. The flight was booked by me about 3 weeks ago at their behest though. My question is what is the most polite way to let them know that I've accepted another offer so won't be coming out, but would like the reimbursement for my airfare? Is their a protocol/good method here?

If you cancel, you will likely get a credit from the airline to use within the year, minus a change fee. I had this happen during my search three years ago, and the school that canceled refunded me the change fee at my request. It doesn't hurt to ask for reimbursement. The only way to do it is to just do it. E.g., thank you for the generous invitation to interview. However, I have already accepted another offer. I know you will need to proceed with the search and offer my spot to another applicant. I have asked the airline for a refund, but there is still a small change fee that I will lose. Would you consider reimbursing me this cost? (If it's too awkward to ask, then you forfeit the money.)

Wow, quite the diversity of opinions. For anyone interested — I told them the situation, and they are reimbursing me for airfare. I was worried about how to approach the subject, as it is awkward for both parties, but let me also express that I think it is completely reasonable to expect at least a partial reimbursement. Two of the opinions in this thread were very anti that sentiment, but I think it also should be recognized that telling the school the situation is the ethically best thing to do, at least in my opinion. As the "anon" before this post stated, lying to a department and still going to the interview for the sake of reimbursement seems like a terrible thing to do — it is a waste of their time, and I am saving them the cost of the hotel, food, incidentals… Thinking about the flip side, what if I went out and they did think I was awesome and they wanted to give me the offer — that is valuable time spent when they could have been considering the other candidates who are still actually on the market. As one of my colleagues mentioned when I discussed this with her, this is part of the job market. Given that interviews are not well timed together, and sometimes are booked a month or more in advance, this situation arises more often then you might think. We, as candidates, are so often wishing that the job interviews were better aligned so that we could make informed decisions, and this seems to be one repercussion of them not at all being aligned in timing. I appreciate that this other department was so kind as to congratulate me on my job offer and cover the cost; I hope that other departments would follow suit, perhaps requiring "evidence" if there is any question about pulling out being for a legitimate reason. That would seem reasonable to me.

Though my situation is resolved, I am curious what others think, given the stark contrasting opinions here so far.

Just a guess by the winky face but I'm willing to bet that was sarcasm. I agree, let them know and try and get money back - what's the worst possible outcome? They say thanks for letting us know but we can't refund you…

Given that we are on the job market and are working with grad student/postdoc/visiting/etc. salaries, interviews can come at quite the literal cost - being out that money would thus be a potential financial challenge. I think asking for reimbursement is fair, esp. since schools almost always tend to request that you purchase airfare immediately, even if the interview is weeks away. It would seem inconsiderate to go on the interview knowing that you wouldn't be accepting - I'm sure the department would want to be aware that one of their candidates is no longer actually a candidate. Job offers are so sparse too nowadays, that I'd hope people who've already met with their success would be happy for us.